An input member of a vehicle transmission receives input torque from a prime mover, e.g., an internal combustion engine or an electric traction motor, and transfers this torque to an output member. The output member in turn powers a drive axle to propel the vehicle through a range of output speed ratios. A typical transmission includes multiple clutches, gear sets, and rotatable shafts. The clutches may be fluid-actuated devices having a friction clutch pack. The clutch pack is selectively engaged using a hydraulic piston.
During the fill phase of a clutch-to-clutch shift, a clutch apply cavity of an oncoming clutch must be rapidly filled with fluid. Torque is transferred from the offgoing clutch to the oncoming clutch in the ensuing torque phase. The oncoming clutch is controlled for a smooth apply during the inertia phase. Coordinated control of the offgoing and oncoming clutches is required to avoid an interruption of power flow through the transmission.